[libcamera-devel] [PATCH v2 2/2] libcamera: ipa_module: Fix implicit sign-extension in elfSection

[Laurent Pinchart]

Hi Umang,

Thank you for the patch.

On Fri, Jun 05, 2020 at 03:09:16PM +0000, Umang Jain wrote:
> Given how the elfSection() is used, the sub-expression
>        (idx * eHdr->e_shentsize)
> has effectively two (16 bits, unsigned) operands.
> The sub-expression is promoted to type int (32 bits, signed) for
> multiplication and then added to eHdr->e_shoff, which is uint32_t
> on 32-bit platforms and uint64_t on 64-bit platforms. Since eHdr->e_shoff
> is unsigned, the integer conversion rules dictates that the other signed
> operand(i.e. the resultant of aforementioned sub-expression) will be
> converted to unsigned type too. This causes sign-extension for both of
> the above operands to match eHdr->e_shoff's type and should be avoided.
> 
> The solution is to explicitly cast one of the operands of the
> sub-expression with unsigned int type. Hence, the other operand will be
> integer promoted and the resultant will also be of unsigned int type,
> not requiring to bother about a sign-extension.
> 
> Reported-by: Coverity CID=280008
> Reported-by: Coverity CID=280009
> Reported-by: Coverity CID=280010
> Signed-off-by: Umang Jain <email at uajain.com>
> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> ---
>  src/libcamera/ipa_module.cpp | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/src/libcamera/ipa_module.cpp b/src/libcamera/ipa_module.cpp
> index f54dd8b..d79151d 100644
> --- a/src/libcamera/ipa_module.cpp
> +++ b/src/libcamera/ipa_module.cpp
> @@ -93,7 +93,8 @@ ElfW(Shdr) *elfSection(Span<uint8_t> elf, ElfW(Ehdr) *eHdr, unsigned int idx)
>  	if (idx >= eHdr->e_shnum)
>  		return nullptr;
>  
> -	off_t offset = eHdr->e_shoff + idx * eHdr->e_shentsize;
> +	off_t offset = eHdr->e_shoff + idx *
> +				       static_cast<uint32_t>(eHdr->e_shentsize);

Is this needed now that idx is an unsigned int and not an uint16_t
anymore ?

>  	return elfPointer<ElfW(Shdr)>(elf, offset);
>  }

-- 
Regards,

Laurent Pinchart